Matteo Reggiani

The performance of gamma- and EtO-sterilised UHMWPE acetabular cups tested under severe simulator conditions. Part 2: wear particle characteristics with isolation protocols

Ultra-high molecular-weight polyethylene (UHMWPE) has been used in total joint replacement for the last three decades. Despite the recent advancements in prosthesis design, the wear of UHMWPE remains a serious clinical problem; the release of wear debris may induce osteolysis and implant loosening. Controlling the quality of the polyethylene is essential to improve its wear resistance and any potential adverse effect caused by processing, manufacturing or sterilisation should be avoided. To evaluate the influence of the sterilisation method (gamma-irradiation and ethylene oxide (EtO)-treatment) and third-body particles, gamma- and EtO-sterilised UHMWPE acetabular cups were tested against CoCrMo femoral heads in a hip joint simulator run for 2.5million cycles in bovine calf serum in the presence of third-body polymethylmethacrylate (PMMA) particles. A method not requiring ultra-centrifugation has been proposed for the isolation of polyethylene wear debris from the serum lubricant. SEM analysis allowed debris shape and morphology to be determined, and the wear mechanism operating in this study to be hypothesised. The morphological features of the wear debris were in agreement with clinical findings, enabling the hip simulator function to be validated. Micro-Raman spectroscopy coupled to PLS analysis showed that the mechanical friction during in vitro tests induced significant crystallinity changes in all the cups. The most significant changes were observed for the EtO-sterilised cups, which showed the highest weight loss.

Determination of crystallinity and crystal structure of Hylamer polyethylene after in vivo wear.

Hylamer™ polyethylene is a crystalline form of polyethylene of 70% crystallinity whereas conventional polyethylene (PE) has 50% crystallinity. Crystallinity is the percentage by weight of the crystalline phase present in the whole polymer, which comprises both amorphous and crystalline phases. Clinical experience has shown that Hylamer™ components used in joint prostheses, if sterilized by gamma rays in the presence of oxygen, are easily affected by wear, which leads to osteolysis. The authors have analyzed the crystallinity of polyethylene liners removed from seven patients who had received Hylamer™ polyethylene implants sterilized by gamma rays in air and had suffered prosthetic loosening, using Raman spectroscopy coupled with partial least squares (PLS) analysis. The results have been compared to those of two controls who had received Hylamer™ polyethylene implants sterilized by gamma irradiation in a nitrogen atmosphere. The crystal structure of wear particles released into the tissues from the Hylamer™ liners sterilized by gamma rays in air is also studied. The materials undergoing two different types of sterilization methods show different crystallinity values (71.50 vs. 69.43), but the crystallinity do not change according to wear (worn and unworn liner region). Both monoclinic and orthorhombic phases are present in the liner, while in wear debris prevalently monoclinic crystals are found in both types of sterilized liners. Different crystallinity rates can explain different wear rates observed in vivo.

In vivo bioactivity of titanium and fluorinated apatite coatings for orthopaedic implants: a vibrational study

Abstract The bone integration of implants is a complex process which depends on chemical composition and surface morphology. To accelerate osteointegration, metal implants are coated with porous metal or apatites which have been reported to increase mineralisation, improving prosthesis fixation. To study the influence of composition and morphology on the in vivo bioactivity, titanium screws coated by Plasma Flame Spraying (PFS) with titanium or fluorinated apatite (K690) were implanted in sheep tibia and femur for 10 weeks and studied by micro-Raman and IR spectroscopy. The same techniques, together with thermogravimetry, were used for characterising the pre-coating K690 powder. Contrary to the manufacturer report, the K690 pre-coating revealed to be composed of a partially fluorinated apatite containing impurities of Ca(OH) 2 and CaCO 3 . By effect of PFS, the impurities were decomposed and the crystallinity degree of the coating was found to decrease. The vibrational spectra recorded on the implanted screws revealed the presence of newly formed bone; for the K690-coated screws at least, a high level of osteointegration was evidenced.

WORKING WITHOUT ACCUMULATION MEMBRANE IN FLOW FFF. EFFECT OF SAMPLE LOADING ON RECOVERY

ABSTRACT Steric/hyperlayer flow field-flow fractionation (St/Hyp/FlFFF) is suitable for the separation and characterization of micrometer-sized particles. In this technique, an ultrafiltration membrane is commonly used as the surface of the accumulation wall. St/ Hyp/FlFFF has been recently tested in membraneless mode and an improvement in performance was found. Recovery was also improved and second-order effects were reduced. In the framework of St/Hyp/FlFFF optimization, the effect of sample loading is a problem of a certain importance. For quantitative purposes, the conversion of peaks into mass particle size distributions is of prime importance and, therefore, the conditions in which there is no effect of sample loading on recovery should be investigated. In this paper, systematic work was performed in order to study the effect of sample loading on recovery. We have found the conditions in which recovery is independent of sample loading. For these conditions, the limit of detection for various micrometer-size standard polystyrene particles was calculated. The absolute sample recovery was calculated by applying a quantitative method for single-run analysis in FFF with UV/Vis detectors.

Isolation and characterization of wear debris generated in patients wearing polyethylene hylamer inserts, gamma irradiated in air

Hylamer polyethylene was used in the early 1990s to make hip-joint components. Clinical experience has shown that these components, if sterilized by gamma rays in the presence of oxygen, are easily affected by wear, which then leads to osteolysis. The authors analyzed polyethylene wear particles in seven patients who had received Hylamer polyethylene implants sterilized by gamma rays in air and had suffered prosthetic loosening. The results were compared to those of six controls, who had received traditional polyethylene implants, sterilized by the same method. The frequency distribution of globular and fibrillar particles was similar in both groups (38.5% in Hylamer, 45.2% in controls). The globular particles in the Hylamer samples had a mean area of 0.12 mm2, which was significantly lesser than that of the controls (0.30 mm2). The width of fibrillar particles in the Hylamer samples was significantly lesser than that of the controls. Therefore, the two materials, despite undergoing the same type of sterilization, produced different types of wear, due to their different properties. In conclusion, the difference in the morphology of Hylamer polyethylene wear particles in comparison with PCA might have caused a more intensive biological response, early and massive osteolysis, and therefore, early loosening.